Carburetors

ABSTRACT

A carburetor of the constant depression type in which liquid fuel is supplied through a fuel metering orifice into a throat defined in the induction passage by an air valve. The effective area of the fuel metering orifice is controlled by a profiled needle carried by the air valve. A transfer passage communicates through a port at one end with the induction passage downstream of the throttle valve when the throttle valve is closed, and, at the other end, with the fuel supply passage between the orifice and the throat through a cavity and a restricted passage. Thus some of the fuel passing through the orifice is passed into the induction passage downstream of the throttle valve when the latter is closed. Air can be drawn from upstream of the throat and mixed with the fuel in the fuel metering orifice to produce an air/fuel emulsion. Air can be fed from a point in the induction passage upstream of the throat and fed to the transfer passage, and valve means may be provided to enable adjustment of the rate of flow of such air fed to the transfer passage.

United States Patent 11 1 Lawrence 1 Aug. 21, 1973 CARBURETORS PrimaExaminer-Tim R. Miles [75] Inventor: Geoffrey Lloyd Lawrence Middlesex,Stanmore England AttorneyStevens, Davis, Mlller & Mosher [73] Assignee:The Zenith Carburetter Company 57 ABSTRACT Limited, Middlesex, England[22] Filed: June 4, 1971 A carburetor of the constant depression type inwhich liquid fuel is supplied through a fuel metering orifice into athroat defined in the induction passage by an air valve. The effectiveApp]. No.: 150,096

"I Foreign Application Priority Data area of the fuel metering orificeis controlled by a 16116 8, 1970 Great Britain 27,627/70 Profiled needlecarried y the air valvo- A transfer passage communicates through a portat one end US. Cl. 261/4411, 261/121 B with the induction Passagedownstream of the Int. Cl. F02m 19/06 throttle valve when the throttleValve is closed Field of Search 261/44 R, 121 B and, at the other end,with the fuel p y Passage between the orifice and the throat through acavity 5 References Cited and a restricted passage. Thus some of thefuel UNITED STATES PATENTS passing through the orifice is passed intothe induction passage downstream of the throttle valve :33; i ;2 whenthe latter is closed. Air can be drawn from 3:278:17l 10/1966 causal 13. 2 61/5O A upstream and m'xed the fuel 3,295,839 l/l967 Mitchel1....261/56 the fuel metering Orifice Pmduce air/fuel 3,342,463 9/1967 p et3] 261/441; emulsion. Air can be fed from a point in the 3,409,27711/1968 Reise 261/51 induction Passage upstream of the throat and fed3,425,672 2/1969 Seigel et a1.... 261/121 B to the transfer passage, andvalve means may be 3,454,264 7/1969 Sarto 261/41 D provided to enableadjustment of the rate of flow FOREIGN PATENTS OR APPLICATIONS Of suchair fed E0 the transfer passage. 119,187 9/1918 Great Britain 261/44 R 6Claims, 2 Drawing Figures Patented Aug. 21, 1973 3,753,555

2 Shoots-Sheet l lllll Patented Aug. 21, 1973 2 Shoots-Sheet 2CARBURETORS This invention relates to carburetors of the constantdepression type, which carburetors are provided, in the inductionpassage thereof, with a throttle valve to control the admission offuel/air mixture to the cylinders of an internal combustion engine towhich the carburetor is connected, and, upstream of the throttle valve,with an air valve operated automatically in accordance with thedepression existing in the chamber defined by the part of the inductionpassage between the throttle valve and the air valve (hereinafter calledthe mixing chamber) so as to control the flow of air, into the saidmixing chamber and maintain a substantially constant depression therein.

In such carburetors, liquid fuel is supplied through a fuel meteringorifice into the induction passage at a position where the effectivearea of the said passage is controlled by the air valve to define athroat in the said induction passage, and thus varies with the degree ofopening of the latter, the effective area of the fuel metering orificebeing controlled by a profiled needle which is moved with the opening ofthe air valve to increase the effective area of the said orifice.Carburetors having the features set out in the two preceding paragraphsare hereinafter termed carburetors of the kind referred to."

It has been found that, in internal combustion engines using carburetorsof this type, idling is not always satisfactory, and it is the object ofthe present invention to provide a carburetor of the constant depressiontype in which more satisfactory idling can be obtained.

According to the invention there is provided a carburetor of the kindreferred to, wherein provision is made for causing a part of the totalfuel flow passing through the fuel metering orifice to pass, when thethrottle valve is closed or substantially closed, into the inductionpassage downstream of the throttle valve.

Preferably, the fuel metering orifice is provided by a restrictedportion of a fuel supply passage leading from a fuel storage chamber tothe throat in the induction passage which restricted portion isconnected to the said throat through a portion of the fuel supplypassage of larger diameter than the said fuel metering orifice.

A fuel transfer passage may be provided which extends from said portionof the fuel supply passage connecting the fuel metering orifice to thethroat to a position in the induction passage downstream of the throttlevalve.

Means may be provided for mixing fuel passing through the fuel meteringorifice, in the said orifice, with air, so that an emulsion of fuel andair is supplied both to the throat and to the induction passagedownstream of the throttle valve.

There will now be described, by way of example and with reference to theaccompanying drawings, two embodiments of carburetors of the constantdepression type embodying the present invention.

In the drawings FIG. 1 is a partial longitudinal section of one form ofcarburetor embodying the invention; and

FIG. 2 is a partial longitudinal section similar to FIG.

-I but showing a modification in which provision is made for admittingextra air to the fuel transfer passage through an adjustable flowrestricting unit. For convenience of drawing, the adjustable flowrestricting unit has been shown in the plane of the section, and thefloat chamber has been omitted, but it will be understood that the saidflow restricting unit would in fact be positioned so as to be clear ofthe float chamber.

Referring to FIG. 1, the carburetor comprises the usual body, part ofwhich is shown at 10, having an induction passage 11 extending throughit. A bridge member 12 formed in the induction passage 1] has a flatsurface 13, chordal to the axis of the passage 11, co-operating with aflat end surface 14 of an air valve slide member 15 movable across thepassage 11 in a direction normal to the flat surface 14 to vary the areaof a throat l6 defined between said bridge member and said slide member.

A butterfly throttle valve 17 is provided in the induction passage 11downstream of the air valve slide 15, and the position of the air valveslide 15 is controlled, in the known manner, by the depression in themixing chamber 18 defined by the part of the induction passage betweenthe said air valve slide 15 and the throttle valve 17.

Fuel is supplied to the induction passage 11 of the carburetor, from afuel supply chamber, partly shown at 19, in which the fuel level iscontrolled by the usual float (not shown), through a jet 21 mounted in abore in the carburetor body 10 opening into the flat surface 13 of thebridge 12, the jet 21 having a bore portion of reduced diameter at 22which constitutes the fuel metering orifice. The said metering orifice22 is spaced from the upper end of the jet 21 by a bore portion 23 oflarger diameter. A profiled needle 24 carried by the air valve slide 15extends through the metering orifice 22 so that the effective area ofthe said orifice varies with the position of the air valve slide.

A flat formed on the exterior of the jet 2] as its upper end defines,between itself and the wall of the bore in the body, a cavity 25connected by a radial passage 26 in the jet to the bore portion 23 abovethe metering orifice 22, and a transfer passage 27, formed in thecarburetor body 10, connects the said cavity 25 to a port 28 openinginto the induction passage 11 at a position such that it is downstreamof, but close to, the edge of the throttle valve 17 when the throttlevalve is closed, the said throttle valve edge passing across the port 28during a very small angle of movement from its closed position.

Thus, when the throttle valve is closed, or nearly closed there is ahigh degree of suction acting on the port 28 and some of the meteredfuel passes directly to the induction passage 11 downstream of thethrottle valve 17, being sucked from the larger diameter bore portion 23of the jet 21 through the radial passage 26, the cavity 25 and thetransfer passage 27, the remainder of the metered fuel passing into thethroat 16 in the usual manner. Due to provision of the cavity 25, thedegree of suction applied to the radial passage 26 is less than thatacting on the port 28 and is dependent upon the volume of the cavity 25,the greater the volume of the cavity 25 the greater the differencebetween the degree of suction acting at the port 28 and the degree ofsuction applied to the radial passage 26. Thus the cavity 25 provides atuning feature. When the throttle valve has opened beyond a certainposition, the suction acting on the port 28 is no greater than thatacting in the throat l6 and substantially the whole of the metered fuelpasses to the throat, the total supply of fuel at all times beingdetermined by the effective area of the jet orifice. When the throttlevalve is closed again,

fuel is drawn initially from the cavity 25 and fed through the transferpassage 27 to the port 28, such initial fluid flow being fed from withinthe cavity 25 at the instant of throttle valve closure, or being fueldrawn into the cavity 25 from the bridge face 13 into which the cavity25 opens. Thus the flow of fuel through the transfer passage 27 isinitiated more quickly than would be so if the transfer passage 27communicated with the larger diameter bore portion 23 of the jet 21solely through the restricted radial passage 26.

A valve (not shown) may be provided in the passage leading from thelateral orifice in the jet to the ports opening into the inductionpassage, to control the flow of fuel in the said passage.

Air is supplied to the fuel metering orifice 22 through an air passage29 opening laterally into the said orifice 22 and receiving air from theinduction passage 11 upstream of the air valve slide 15, so that anair/fuel emul sion is formed in the jet 21, and it is this air/fuelemulsion which is supplied to the induction passage 11 downstream of thethrottle valve 17. The air passage 29 preferably leads downwardly to itsconnection with the fuel jet, to reduce the risk of fuel being depositedin the said passage which could prevent the emulsion air bleed fromworking.

The provision of an air supply to the fuel metering jet as abovedescribed is more fully described and is claimed in our co-pendingApplication No. 55836.

In the embodiment of the invention shown in FIG. 2 of the drawings,provision is made for supplying extra air to the transfer passage to mixwith the fuel or fuellair emulsion passing through that passage. In myearlier filed United States patent application Ser. No. 127,206, filedMar. 23, 1971 (executed March 15, i971), also entitled IMPROVEMEIXIS INOR RE- IJATING TO CARBURETORS, I have described and claimed a carburetorof the kind to which the present invention relates, wherein a furtherpassage provided for supplying air directly to the induction passage ata position downstream of the throttle valve, when the said throttlevalve is in the idling position, is so controlled by operation of thethrottle valve that the supply of air through said further passage tothe induction passage downstream of the throttle valve ceases when thesaid throttle valve has in the arrangement shown in FIG. 2 of theaccompa nying drawings, in which parts corresponding to those shown inFIG. I, bear the same reference numerals, a further passage as describedin my said earlier filed application is provided by the part of thetransfer passage 27 adjacent the port 28, and an air supply passageconnected into the said transfer passage.

The said air supply passage comprises a part 31 leading from theinduction passage 11 upstream of the air valve slide to an adjustableflow restricting unit 32, and a part 33 leading from the said unit 32into the transfer passage 27, the said unit 32, although shown in thesection plane in FIG. 2, being in practice, arranged in some otherposition around the axis of the induction passage so as to be clear ofthe float chamber, which is not shown in FIG. 2.

The flow restricting unit 32 has formed in it a first passage 34connecting with the air supply. passage part 31, a second passage 35,parallel to the passage 34 and closed at one end, a third passage 36connecting the other end of the passage 35 to the passage 34, and afourth passage 37 connecting the passages 34 and 35 which is connectedintermediate its ends, by a fifth passage 38, to air supply passage part33.

A screw plug 39 mounted in a screw-threaded bore aligned with thepassage 36 has a tapered end 41 seating in the passage 36 and is formedwith intersecting bores 42, 43 providing a fixed flow restrictionbetween the passages 34 and 35, and a second screw plug 44, mounted in ascrew-threaded bore 45 aligned with the passage 37, has tapered portions46 and 47 cooperating respectively with the parts of the passage 37 onopposite sides of the passage 38 to provide an ad justable restrictionof flow between the passages 34, 35 and the passage 38. Thus the actualrate of flow of air through the passage 31,33 is determined by the areaof the bores 42, 43 in the plug 39, and the position of each of thetapered portions 46 and 47 relative to the respective parts of thepassage 37 with which they co-operate. The rate of flow of air can bevaried by movement of the screw plug 44 in or out to alter the positionof the tapered portions 46 and 47 relative to the respective parts ofthe passage 37 with which they co-operate. The degree of control of theactual rate of flow of air through the passage 31, 33 which can beachieved by movement of the screw plug 39 is related to the position ofthe screw plug 44, and the extent by which movement of the screw plug 39can effect the rate of flow of air for a particular position of thescrew plug 44 is limited to a minimum value by the area of the bores 42and 43, and to a maximum value by the position of the tapered portion 47relative to the respective part of the passage 38 with which itco-operates.

It has been found that the provision of the transfer passage 27 hasadditional advantages in that, by reason of its connection to theinduction passage 11 downstream of the throttle valve, a higher suctionis applied to the air/fuel emulsion supply system than would 0therwisebe the case. This higher suction has been found to exercise astabilizing influence on the action of the air/fuel emulsion supplysystem particularly in regard to the initiation of air flow to the fueljet.

I claim:

1. A carburetor of the constant depression type comprising:

a. a body having an induction passage which extends therethrough;

b. a throttle valve connected within the induction passage;

c. an air valve in the induction passage upstream of said throttlevalve, said air valve defining a throat area within the inductionpassage, said body also having an opening into the throat area;

d. a fuel supply jet, located in the opening, having a fuel meteringorifice wherein fuel is fed to said orifice, said fuel supply jet alsoincluding a bore, having a larger diameter than said orifice, throughwhich fuel flows from said orifice to said throat;

. first means for supplying air to said fuel metering orifice to form anemulsion of air and fuel in said orifice; and

f. a fuel transfer passage having one end open to said bore and theother end open to said induction passage downstream of said throttlevalve, whereby when said throttle valve is substantially closed part ofthe fuel-air mixture will be supplied to said throat and part will besupplied through said fuel transfer passage downstream of said throttlevalve.

5. The carburetor according to claim 1 wherein said one end of said fueltransfer passage has a cavity open to said throat and a radial passageextending from said cavity and open to said bore whereby said fuelsupply passage receives a fuel-air mixture from said throat and fromsaid fuel supply jet.

6. The carburetor of claim 1 wherein said first air supply meanscomprises an air supply passage which slopes downward to said orifice.

1. A carburetor of the constant depression type comprising: a. a bodyhaving an induction passage which extends therethrough; b. a throttlevalve connected within the induction passage; c. an air valve in theinduction passage upstream of said throttle valve, said air valvedefining a throat area within the induction passage, said body alsohaving an opening into the throat area; d. a fuel supply jet, located inthe opening, having a fuel metering orifice wherein fuel is fed to saidorifice, said fuel supply jet also including a bore, having a largerdiameter than said orifice, through which fuel flows from said orificeto said throat; e. first means for supplying air to said fuel meteringorifice to form an emulsion of air and fuel in said orifice; and f. afuel transfer passage having one end open to said bore and the other endopen to said induction passage downstream of said throttle valve,whereby when said throttle valve is substantially closed part of thefuel-air mixture will be supplied to said throat and part will besupplied through said fuel transfer passage downstream of said throttlevalve.
 2. The carburetor according to claim 1 further comprising secondmeans incuding an air supply passage for supplying extra air to the fuelflowing from said fuel metering orifice and entering the inductionpassage downstream of said throttle valve.
 3. The carburetor accordingto claim 2 wherein said extra air supply passage is connected to saidfuel transfer passage.
 4. The carburetor according to claim 2 whereinsaid extRa air passage includes an adjustable flow restricting unit forcontrolling the flow of extra air.
 5. The carburetor according to claim1 wherein said one end of said fuel transfer passage has a cavity opento said throat and a radial passage extending from said cavity and opento said bore whereby said fuel supply passage receives a fuel-airmixture from said throat and from said fuel supply jet.
 6. Thecarburetor of claim 1 wherein said first air supply means comprises anair supply passage which slopes downward to said orifice.